In chemical vapor deposition techniques, reactions sometimes vary over a workpiece surface such as over a semiconductor wafer. For example, surface topography such as interconnect vias or trenches can exhibit different reaction rates at the top of the features compared to within the vias, trenches, etc. It is often desirable to reduce reaction rate variances to provide what is referred to as uniform step coverage. The desired result is a deposited material layer of uniform thickness over all surface topography. In other situations, it is desirable to selectively control or substantially eliminate reaction rates in one region, for example on a surface of a semiconductor wafer, in comparison to within a feature such as a trench or via, etc. It is also desirable to control reaction rates with more precision than existing techniques such as controlling flow rates of chemical vapor deposition components.
Atomic Layer Deposition (ALD) is one form of chemical vapor deposition (CVD) that is used with the desire to achieve conformal films. Some technical hurdles with ALD and CVD in general involve insufficient precursor flux at the bottom of trenches; precursor decomposition at the top of trenches; incomplete reactant gas separation leading to CVD at the top of the trench; or readsorption of reaction products leading to site blocking at the bottom of the trench. These mechanisms may also lead to non-uniformity in batch and traveling wave ALD or CVD reactions.
What is needed is an improved method of CVD and/or ALD that addresses these and other concerns.